1. Field of the Invention
The present invention relates to a printing apparatus with a forme cylinder. The forme cylinder has in its interior a first roller for winding off a printing foil which can be pulled onto the outer surface of the forme cylinder, and a second roller for winding up the printing foil which has been pulled onto the outer surface of the forme cylinder.
The invention additionally relates to methods of preparing the forme cylinder for printing.
2. Description of the Related Art
Xerox Disclosure Journal, Volume 1, Number 4, Page 19 (1976), discloses the use of a thin exchangeable printing foil in lithographic printing processes. The printing foil is stored in the interior of a forme cylinder of a printing apparatus. The forme cylinder has in its interior a first and a second roller, and the printing foil which has not yet been used is wound onto the first roller and the printing foil which has been used for printing is wound onto the second roller. The first roller is accommodated within an interior space of the forme cylinder which is connected through a first opening with the outer surface of the forme cylinder. The printing foil exits through this first opening from the first roller onto the outer surface of the forme cylinder, the printing foil is then wound once around the forme cylinder and enters through a second opening a second interior space which contains the second roller. In this printing apparatus, it is possible that the printing foil which is on the outer surface of the forme cylinder contains an image to be printed and, after the foil has been used, is wound up from the outer surface of the forme cylinder onto the second roller, while simultaneously printing foil is wound from the first roller onto the outer surface of the forme cylinder. The printing foil which now covers the outer surface of the forme cylinder forms the foundation for a lithographic writing process which is used to apply a new image to be printed onto the printing foil, for example, by means of a laser writing system.
The known printing apparatus has the disadvantage that the outer surface of the forme cylinder has two openings, so that the smaller of the two area portions of the outer surface resulting from the two openings cannot be utilized for the printing process because this area portion is not covered with printing foil.